Influences of seasonal source waters on changing Arctic hydrology

The warming climate in the Arctic terrestrial regions resulted in earlier snowmelt in spring, deeper active layer thickness, and larger rainfall in the summer season. These changes have driven the changes to higher summer evapotranspiration and increased river discharge in autumn and the cold season, evidently indicating shifts in the seasonal hydrological processes. Very few studies have provided quantitative assessments of changes in the seasonal hydrological processes, including contributions of the seasonal source waters (i.e., snow, rain, and ground ice water) to the changes. A land surface model, coupled with a tracer scheme tracking along the flow route of individual source waters in the hydrological processes, was used to assess the changes in the pan-Arctic water budget for the past four decades. The model results showed that summer-sourced rainwater contributed to the increases in summer evapotranspiration and autumnal river discharge during the study period. In addition, the autumn rainwater was connected to the peak river discharge and evapotranspiration in the spring of the following year, suggesting a soil-water memory effect that the autumnal rainfall, stored as frozen soil water during the winter season was reactivated at the spring season with soil thawing. The permafrost degradation-induced ground ice meltwater showed a weak relationship with the increasing river discharge. This model study provides a possibility to distinguish quantitatively the changes in the Arctic ecohydrological processes, resulting from the future climate warming.